The present invention relates to a joint device for correcting a structural member in a space truss structure and, more particularly, to a device capable of easily and tightly connecting a plurality of long steel pipes to nodes in the space truss structure.
In a space truss structure each steel pipe is joined at a node by a fastening bolt mounted in an end cap closing the respective pipe. The fastening bolt is axially slidable in a sleeve disposed between a spherical node and the end cap, provided with a first external threaded part engaging a screw hole in the node, a second external threaded part engaging an anchor nut in the steel structural pipe and a polygonal boss formed on an intermediate portion thereof. Rotation of the sleeve, slidably engaged with the polygonal boss, joins the steel pipe to the node.
A sufficient protrusion of the first external threaded part beyond an end of the sleeve is required to engage the first threaded part with the screw hole of the node, e.g., one or two threads, substantially 3 to 5 mm. Upon completion of assembly of most portions of the truss, positions of nodes to which a final structural pipe member is to be joined are established. Thus, the protrusion of the first threaded part hinders fitting the final structural pipe member into the space between the nodes, since the distance therebetween has already been defined.
U.S. Pat. No. 4,872,779 discloses a joint device for fitting a steel pipe between unmovable nodes by temporarily retracting a fastening bolt back into a sleeve. The device is provided with a coiled spring, compressed when an end of a threaded part of the fastening bolt contacts the node, which biases the fastening bolt toward a screw hole in the node the distance necessary for an initial engagement of the two parts.
Since the joint device is equipped with a coiled spring and a sleeve nut to mount the fastening bolt in addition to a fastening bolt and a sleeve, the number of parts and the amount of thread cutting increase. Also, accommodation of a coiled spring in the sleeve requires the device be longer and/or larger.
A device without a coiled spring is disclosed in U.S. Pat. No. 5,141,351. A fastening bolt has an outside thread formed on each of a plurality of longitudinal edges of a polygonal boss which engage an internal thread formed on an inner face of a bore in an end cap, the pitch of which is identical to that of a first threaded part of the fastening bolt.
Reverse rotation of the sleeve put on the boss partially engaging the internal thread permits an end of the fastening bolt to be retracted into the sleeve. Positively rotating the sleeve advances the fastening bolt to the node by engagement of the outside thread with the internal thread, permitting the end of the first threaded part to enter a screw hole of the node.
A diameter of the internal thread in the end cap is increased because of the engagement with the outside thread of the polygonal boss, thus increasing the amount of thread cutting and decreasing the strength of the end cap. Adding thickness to the end cap for strengthening results in an increase in weight.
The above device has a bolt head instead of an anchor nut as used in the device of U.S. Pat. No. 4,872,779 to maintain the end of the fastening bolt inside the end cap. A fastening bolt provided with a bolt head is applicable to a joint device for heavy loads since it has no second threaded part which is substantially smaller than the shank of a fastening bolt. However, use of a bolt head requires thick material for manufacturing a fastening bolt with a large bolt head. As a result, the amount of machining increases as do expenses.
The sleeve and the fastening bolt are shipped to a construction site after they are integrated with steel pipes in the manufactory. Although the sleeve is put on the fastening bolt, it is slidable along the polygonal boss thereof and is not locked on the end of a steel pipe. The structural pipes are intentionally or unintentionally inclined during transportation to desired nodes by lifting machinery. Thus, construction of a truss is interrupted if the sleeves fall off the fastening bolts.
To solve the problem, each sleeve is temporarily fixed to the respective steel pipe by adhesive tapes etc. prior to transport to the site or hoisting to the constructing space. It is inconvenient for workers to remove the tape just before the rotation of the sleeve for connecting the steel pipe to the node.